This invention relates to a photocatalytic reactor system for the reduction of contaminants, typically sulfur dioxide, in flue effluents which may reduce or eliminate acid rain caused by the emission of sulfur dioxide produced by high sulfur fuels. This invention will permit the use of high sulfur coals such as certain bituminous coals, which are more abundant, higher in energy content, and lower in cost. In addition, the photocatalytic reactor system of this invention is simpler in construction and therefore lower in cost, both in cost of production and operation, than conventional methods. Additionally, the photocatalytic reactor of this invention can produce a useful and salable by-product.
Fossil fuel combustion, such as used in power generation plants, results in effluent streams containing numerous contaminants, including sulfur dioxide. In the upper atmosphere, sulfur dioxide converts to sulfur trioxide which readily combines with water to form sulfuric acid, a major component of acid rain.
Conventional methods for removing contaminants from flue effluents are very large, complex, and expensive systems to purchase and operate, and produce wastes with high disposition costs. There are five problems associated with such known systems and methods.
The first problem is that conventional reactors cannot effectively remove sulfur dioxide from the effluent that comes from burning high sulfur content coal.
The second problem is the complexity and high operational expenses of current sulfur dioxide reduction methods, which commonly require the use of expensive catalysts, e.g. vanadium pentoxide.
The third problem is the requirement to use lower sulfur content coal in order for conventional effluent treatments to effectively meet current environmental regulations. Current EPA regulations for commercial and industrial sources specify that xe2x80x9cAny coal, oil, or mixture thereof, burned in any fuel burning or process installation not covered by New Source Performance Standards for sulfur emissions shall contain no more than 1.0 pound sulfur per million gross BTU heat input for any mixture of coalxe2x80x9d (R307-203-1). Using as an example Northern Appalachian region coalsxe2x80x94less than 5% of raw coal samples burned would comply with this standard. The raw coal would need to be pre or post-combustion treated. For Midwest region coals, less than 1% of raw coal samples burned will comply with the EPA regulations.
The fourth problem lies in the use of higher sulfur content coal, as it must be pre-cleaned in such a way as to reduce its sulfur content. Of the mineral impurities found in coal, sulfur is the most important single element impeding the utilization of coal as a clean fuel. For example, the coal fields of Illinois, Indiana and western Kentucky contain 29% of the estimated remaining bituminous coal reserves of the United States. However the coals from these states tend to have high organic sulfur content. Approximately 80% of the reserve has a sulfur content of greater than 3%. As shown in FIG. 1, the current EPA standard is represented by line 7. Lines 1, 2 and 3 show the pounds of sulfur dioxide emitted per million Btu for northern Appalachian coal fired raw (1), crushed to 14-mesh top size (2) and crushed to 1xc2xdxe2x80x3 top size (3). Similarly, lines 4, 5 and 6 show the data for Midwestern coal fired raw (4), crushed to 14-mesh top size (5) and crushed to 1xc2xdxe2x80x3 top size (6). See Eliot, Robert C., Coal Desulphurization Prior to Combustion, Noyes Pub., December, 1978. The technology exists today to clean high sulfur content coals prior to combustion, but depending on the level of preparation required, this can add significant cost to the coal delivered.
The fifth problem is that a substantial amount of an electric power plant""s output is needed to run conventional catalytic reactors thereby decreasing the overall efficiency of the plant.
These known systems all convert sulfur dioxide to sulfur trioxide as it is easier to separate sulfur trioxide from the effluent stream. Numerous conventional techniques exist to remove sulfur trioxide from the effluent stream, including limestone gypsum wet scrubbing, sea water washing, ammonia scrubbing, spray-dry process, and sodium bicarbonate injection process. These techniques are described in U.S. Pat. Nos. 5,791,268; 5,997,823; 6,063,348; and 6,303,083.
It is therefore an object of this invention to provide a photocatalytic reactor system that can effectively remove sulfur dioxide from the smoke that comes from burning high sulfur content coal.
It is a further object of this invention to provide a less complex and more cost effective reactor than the current technology and to provide such a reactor that is simpler in design and therefore more reliable to operate and has lower operational costs.
It is a further object of this invention to enable the use of types of coal that were formerly unusable due to their high sulfur content and thereby increase non-petroleum energy reserves.
It is a further object of this invention to enable the use of types of coal that were formerly too expensive to use due to the cost of pre-combustion cleaning and thereby increase non-petroleum energy reserves.
It is a further object of this invention to provide a reactor that takes less of a power plant""s energy to operate and increase the saleable output of the power plant and therefore decrease the cost of electricity to consumers.
It is a further object of this invention to provide such a photocatalytic reactor system which is readily integrated into existing effluent streams.
The invention results from the realization that sulfur dioxide converts to sulfur trioxide as a spontaneous reaction in the upper levels of the atmosphere in the presence of solar radiation and that, by adding photonic radiation to the effluent stream, this reaction can be made to occur efficiently and rapidly before the effluent stream is released into the atmosphere. Photonic energy can produce a variety of reactions necessary and useful in treating and reacting flue gas or other effluents. Such photonic energy can be easily introduced into the effluent stream with sufficient intensity to produce a useful reaction; that the reactor vessel can be a simple design with few or no moving parts to make it highly competitive with existing technology; that the photonic energy can be combined with reactive or inert reactants, and their chemical counterparts, to produce a variety of reactions necessary and useful in treating contaminants in flue effluent or other reactants; that the reaction efficiency is higher than is currently available from conventional effluent treatment technologies; that the reaction chambers can be provided in different sizes and geometries to produce specific reactions; and that the reaction chambers may be configured in parallel or series or a combination of the two in order to react with a greater quantity or flow of effluent.
This invention features a photocatalytic reactor system for treating flue effluents containing at least one contaminant including at least one reactor vessel, an effluent inlet connected to the reactor vessel for receiving an effluent stream, at least one photonic energy source coupled to the reactor vessel for introducing photonic energy into the effluent stream, and an effluent outlet connected to the reactor vessel for discharging a treated effluent stream. The photonic energy catalyses a reaction in the effluent stream to reduce contaminant emissions.
In a preferred embodiment, photonic energy source may be a laser or a lamp. The photonic energy source may include an ultraviolet (UV) energy source.
The photocatalytic reactor system may include a plurality of reactor vessels connected in parallel, series, or in a matrix of parallel and series configurations to react with a greater flow of the effluent stream. The reactor vessel may be cylindrical, spherical, quadrangular or any other suitable shape.
The contaminant in the effluent stream may be sulfur dioxide, and the sulfur dioxide may be converted to sulfur trioxide by the photonic energy.
A reactant inlet may be connected to the reactor vessel for injecting at least one reactant into the reaction vessel. The reactant may be an inert gas or inert chemical or chemical mixture. The reactant may be a reactive gas or a reactive chemical or chemical mixture. The reactant may, for example, accelerate the conversion of sulfur dioxide to sulfur trioxide.
The photocatalytic reactor system may also include a plurality of photonic energy sources connected to the reactor vessel for increasing the amount of photonic energy introduced into the effluent stream.
This invention also features an ultraviolet catalytic reactor system for treating an effluent stream containing at least one contaminant including at least one reactor vessel, an effluent inlet connected to the reactor vessel for receiving the effluent stream, at least one ultraviolet energy source coupled to the reactor vessel for introducing ultraviolet energy into the effluent stream, and an effluent outlet connected to the reactor vessel for discharging a treated effluent stream. The ultraviolet energy catalyzes a reaction in the effluent stream to reduce contaminant emissions.
In a preferred embodiment, the ultraviolet energy source may be a laser or a lamp. There may be a plurality of reactor vessels connected in parallel, series or a combination of parallel and series configurations to react with a greater flow of the effluent stream. The reactor vessel may be cylindrical, spherical, quadrangular or any other suitable shape.
The contaminant in the effluent stream may be sulfur dioxide, and the sulfur dioxide may be converted to sulfur trioxide by the ultraviolet energy. The ultraviolet catalytic reactor system may also include a reactant inlet connected to the reactor vessel for injecting a reactant into the reaction vessel. The reactant may be an inert gas, an inert chemical or chemical mixture, a reactive gas, or a reactive chemical or chemical mixture. The reactant may accelerate the conversion of sulfur dioxide to sulfur trioxide.
The photocatalytic reactor system may also include a plurality of photonic energy sources connected to the reactor vessel for increasing the amount of photonic energy introduced into the effluent stream.
This invention also features an ultraviolet catalytic reactor system for treating an effluent stream containing at least one contaminant including at least one reaction chamber including an annular ring including a first opening for receiving an effluent stream and a second opening for discharging a treated effluent stream, a plurality of ultraviolet energy inlets in the annular ring for introducing ultraviolet energy into the effluent stream, and at least one ultraviolet energy source connected to the plurality of ultraviolet energy inlets. The ultraviolet energy catalyzes a reaction in the effluent stream to reduce contaminant emissions.
In a preferred embodiment, the ultraviolet energy source may be connected to the plurality of ultraviolet energy inlets by a plurality of optical fibers. The ultraviolet energy source may be a laser or a lamp. The annular ring may include a plurality of injection nozzles for injecting a reactant into the reaction chamber. The plurality of injection nozzles may be connected to a manifold for delivery of the reactant. The reactant may be an inert gas, an inert chemical or chemical mixture, a reactive gas, or a reactive chemical or chemical mixture.